In recent years it has, in many countries, been a requirement that all new toilet cisterns installed should have a dual-flush function, in which a full flush releasing a large quantity of flushing liquid can be used when solid waste is to disposed of and a partial flush releasing a smaller quantity of flushing liquid can be used when a full flush is not required, for example, when liquid waste is to be disposed of.
Many such mechanisms for dual flush cisterns have been proposed.
In certain systems the cistern is divided into two parts by a weir having a movable gate such that when a partial flush is required the gate remains closed and only the liquid on one side of the weir is released through the cistern outlet but when a full flush is required the gate is opened allowing liquid on both sides of the weir to pass through the outlet. Examples of such dual flush mechanisms are disclosed in AU-B-56165/80 and WO93/15284.
Another type of dual flushing mechanism relies on closing the outlet valve after different times depending on whether a full or partial flush is required.
Examples of such mechanism are described, for example, in AU-A-28538/84, AU-B-80111/87, AU-B-40396/85 and WO93/15284.
The prior art mechanisms generally include a float assembly comprising a float associated with the valve stem of the outlet closure valve and either attached to or slideable on the valve stem. The float reduces the negative buoyancy of the float assembly so that the float assembly sinks at a slower rate to close the valve than it would do if the float were not present.
The majority of the prior art mechanisms include a large number of moving parts and are complicated in their structure in that various non-linear motions are involved in operation of the valve.
It is the object of this invention to provide a flushing mechanism for a dual flush cistern that is very much simpler than the existing mechanisms.
This invention provides a dual flush system comprising a float assembly comprising a hollow valve stem carrying a sealing valve for sealing the outlet opening of the cistern at or towards one end and being open at each end to define an overflow passage and a float fixedly attached around the valve stem, a cylindrical guide member surrounding the float and having at the end adjacent the sealing valve at least one opening to allow liquid to pass to the outlet opening, an operating rod arranged to move vertically upward to raise the float assembly to open the valve, first and second operating means arranged to effect such vertical movement of the operating rod, the first operating means, on operation, being arranged to raise the float assembly a first distance, and the second operating means being arranged to raise the float assembly a second distance less than the first distance, whereby when the first operating means is operated and released, a first predetermined quantity of liquid flows from the cistern, and when the second operating means is operated and released a second, smaller, predetermined quantity of liquid flow from the cistern.
The float preferably comprises an inverted cup-shaped member which traps air, thereby reducing the negative buoyancy of the float assembly. The rate of closing the valve is dependent on the hydrostatic pressure acting on the float and on the distance that the float has to move to close the valve. Thus, the float assembly is designed so that when the float assembly is raised by the first, full flushing, distance the float is buoyant and so falls to close the valve as the level of the liquid supporting it drops thereby allowing the predetermined quantity of liquid to flow from the cistern. However, when it is raised by the second, partial flushing, distance the hydrostatic pressure on the float surface is such that the float is not buoyant and the valve starts to close as soon as the operating means is released the rate of closure being such that the second predetermined amount of liquid flows from the cistern.
In some instances for example when the operating means is held down for too long a time or is operated too violently the water level in the cistern may drop so far or the float assembly may gain sufficient momentum to move further upward than the second predetermined distance that the assembly may become buoyant. Preferably, therefore, the second operating means, on operation, in addition to raising the float assembly also operates a stop mechanism acting on some part of the float assembly to prevent movement of the float assembly greater than the second distance in its simplest form, such stop mechanism comprises a rod which on operation of the second operating means, is introduced into the float guide member to a predetermined level to contact the upper surface of the float when the float has reached the desired height. Preferably, the stop mechanism is adjustable to allow fine-tuning of the quantity of liquid that flows from the cistern in a partial flush. This may be achieved by means of a screw thread on the road by means of which the lower end of the rod can be raised or lowered relative to the float. The rod preferably passes through a guide member mounted on the rim of the float guide member in order to constrain movement of the rod only to an up and down movement.
The operating means preferably comprises a pair of push buttons on the top of the tank, depression of which moves a pivoted fever which is connected to the operating rod. However, especially when the mechanism is intended for use as a conversion kit for an existing lever operated cistern the operating means may comprise a pair of levers, for example mounted on concentric shafts with appropriate linkages to the operating rod.
The operating mechanism is preferably carried on a bracket which is mounted on the side of the float guide means, the length of which is preferably adjustable to allow the mechanism to be used in cisterns of different height. In a mechanism in which the length of the bracket is adjustable the length of the operating rod end of the stop rod, when present must also be adjustable.
Preferably the second operating means, on operation, in addition to raising the float assembly, also operates a stop mechanism acting on some part of the float to prevent movement of the float a distance greater than the second distance. The stop mechanism is preferably a rod which on operation of the second operating means is introduced into the float guide member to contact the upper surface of the float when the float has reached its desired height.
In a preferred form of the operating mechanism, the connection between the operating means and the float assembly, comprises a rod or bar with a plurality of spaced holes at least at its end adjacent to the float assembly which cooperates with a bracket on the float guide member which also has at least one hole through which a fixing pin can be passed into one of the holes on the bracket. The operating rod and the stop rod may be telescopic and maybe held together by locating pins which can pass through locating holes, as necessary. In the case of the stop rod, the rod is preferably mounted in a U-shaped rod carrier and the locating pins are permanently attached to the rod sot that the rod can be rotated to snap the pin into and out of one of a plurality of notches on the rod carrier. The rod carrier may be mounted by a screw thread on the second operating means to allow fine adjustment of the effective length of the rod.